I bought Cineform's Neoscene software a month or so back to edit my HDV and AVCHD video. Basically you feed those formats to it, it spits out a Cineform AVI that's readable by most popular editing programs. No more stuttering playback while editing. The downside is the files are big, 30-40gb/hour big, but storage is perpetually larger and cheaper, and besides when you're through editing you don't have to keep them anyway, you still have your originals.
The big news is this past week Cineform has released an upgrade to Neoscene that will convert Canon 5d2 video to cineform avit. Looks like the first rollout still didn't fix the crushed blacks, but the newest version has. I haven't had a chance to upgrade and try it with any 5d2 video yet, but if it works like it does on the HDV and AVCHD video I have used it on i'd say it's definately worth looking into for a lot of folks. You can get a free 7 day trial. I see it's It's $100 at Videoguys.com, probably it's a download, that's the way mine was when I bought it. A small download and then they sent you the activation code.
There may be some free ways to do the same thing but I'm lazy these days and like that I just toss a folder full of files at this thing, come back an hour or two later and have a way bigger folder full of files that are easy to edit.
There's threads in the 5d2 as well as Cineform sections on dvinfo.net discussing the software. Oh and there's an Apple version as well.